U.S. patent application number 11/002874 was filed with the patent office on 2005-06-30 for vsb receiver and carrier recovery apparatus thereof.
This patent application is currently assigned to LG Electronics Inc.. Invention is credited to Kim, Joon Tae, Kim, Tok.
Application Number | 20050141645 11/002874 |
Document ID | / |
Family ID | 34703412 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050141645 |
Kind Code |
A1 |
Kim, Joon Tae ; et
al. |
June 30, 2005 |
VSB receiver and carrier recovery apparatus thereof
Abstract
There are provided a VSB receiver and a carrier recovery
apparatus thereof, in which a carrier is recovered using a VSB
modulated signal. In the VSB receiver, a digital processing part
selects a desired channel frequency through an antenna, converts
the channel frequency into an intermediate frequency, and
digitalizes the channel frequency by passing a predetermined band
of the intermediate frequency. A carrier recovery part extracts
pilot signals by using a first LPF having a first bandwidth and a
second LPF having a second bandwidth, and recovers a baseband
carrier wave signal from a passband signal by using one of the
extracted pilot signals. A clock demodulation part removes the
pilot signal from the baseband carrier wave signal and extracts a
synchronizing signal. A noise removing part removes a linear noise
and a residual phase jitter of the baseband signal by using the
synchronizing signal. A decoding part decodes the baseband signal
whose noise is removed. Accordingly, the carrier recovery can be
stably performed even when the pilot signal is weak.
Inventors: |
Kim, Joon Tae; (Yongin-si,
KR) ; Kim, Tok; (Seoul, KR) |
Correspondence
Address: |
JONATHAN Y. KANG, ESQ.
LEE, HONG, DEGERMAN, KANG & SCHMADEKA
14th Floor
801 S. Figueroa Street
Los Angeles
CA
90017
US
|
Assignee: |
LG Electronics Inc.
|
Family ID: |
34703412 |
Appl. No.: |
11/002874 |
Filed: |
December 1, 2004 |
Current U.S.
Class: |
375/326 ;
348/E5.093; 348/E5.108; 348/E5.113 |
Current CPC
Class: |
H04L 1/004 20130101;
H03D 1/24 20130101; H04L 2027/0067 20130101; H04N 5/4401 20130101;
H04L 27/066 20130101; H04N 21/426 20130101; H04L 2027/0087
20130101; H04L 2027/0028 20130101; H04L 2027/0057 20130101; H04N
5/455 20130101; H04L 2027/0069 20130101; H04N 5/38 20130101 |
Class at
Publication: |
375/326 |
International
Class: |
H04L 027/22 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2003 |
KR |
10-2003-0086336 |
Dec 22, 2003 |
KR |
10-2003-0094592 |
Claims
What is claimed is:
1. A VSB (vestigial sideband) receiver for use in a digital TV
receiver for demodulating a passband analog signal into a baseband
digital signal, the VSB receiver comprising: a digital processing
part for selecting a desired channel frequency through an antenna,
converting the channel frequency into an intermediate frequency,
and digitalizing the channel frequency by passing a predetermined
band of the intermediate frequency; a carrier recovery part for
extracting pilot signals by using a first LPF having a first
bandwidth and a second LPF having a second bandwidth, and
recovering a baseband carrier wave signal from a passband signal by
using one of the extracted pilot signals; a clock demodulation part
for removing the pilot signal from the baseband carrier wave signal
and extracting a synchronizing signal; a noise removing part for
removing a linear noise and a residual phase jitter of the baseband
signal by using the synchronizing signal; and a decoding part for
decoding the baseband signal whose noise is removed.
2. The VSB receiver of claim 1, wherein the carrier recovery part
further includes: a comparator for comparing powers of pilot
components passing through the first and second LPFs; a selector
for selecting one of the pilot components extracted from the first
and second LPFs according to the comparison result of the
comparator.
3. The VSB receiver of claim 2, wherein the comparator compares a
first threshold value (lock1) and a second threshold value (lock2),
the first threshold value (lock1) being generated from a first
carrier recovery part using the first LPF, the second threshold
value (lock2) being generated from a second carrier recovery part
using the second LPF.
4. A carrier recovery apparatus comprising: a complex multiplier
for multiplying a digitalized passband signal by an oscillation
frequency of an oscillator and outputting a recovered carrier wave
of a baseband signal; a first band pilot signal and frequency/phase
error detecting part for outputting a pilot signal component and a
frequency/phase error component of a first bandwidth, the first
bandwidth being a bandwidth of an LPF for extracting a typical
pilot signal contained in the baseband signal outputted from the
complex multiplier; a second band pilot signal and frequency/phase
error detecting part for outputting a pilot signal component and a
frequency/phase error component of a second bandwidth among the
baseband signals outputted from the complex multiplier, the second
bandwidth being narrower than the first bandwidth; a comparing part
for comparing the pilot signal components outputted from the first
and second band pilot signal and frequency/phase error detecting
parts, and outputting a selection signal for selecting one of
output results of the first and second pilot signal and
frequency/phase detecting parts; a selecting part for selecting one
of the frequency/phase error components outputted from the first
and second band pilot signal and frequency/phase error detecting
parts, based on the selection signal of the comparing part; a loop
filter for removing an RF component contained in the selected
frequency/phase error component; and an oscillator for changing an
oscillation frequency according to the frequency/phase error
component whose RF component is removed.
5. The carrier recovery apparatus of claim 4, wherein the first
band pilot signal and frequency/phase error detecting part
includes: a first LPF, a first delay unit and a first code
detector, which are configured to form a loop for receiving a
baseband I signal from the complex multiplier and detecting the
pilot signal component and the frequency error component of the
first bandwidth; a second LPF configured to form a loop for
receiving a baseband Q signal from the complex multiplier and
detecting a phase error of the first bandwidth; a first multiplier
for multiplying the frequency error by the phase error and
detecting a frequency/phase error; and a first integrator for
accumulating power of the pilot signal component outputted from the
first code detector, and generating a lock signal to the comparing
part if the accumulated power of the pilot signal component reaches
a preset pilot power threshold value, wherein the second band pilot
signal and frequency/phase error detecting part includes: a first
LPF, a second delay unit and a second code detector, which are
configured to form a loop for receiving the baseband I signal from
the complex multiplier and detecting the pilot signal component and
the frequency error component of the second bandwidth; a second LPF
configured to form a loop for receiving the baseband Q signal from
the complex multiplier and detecting a phase error of the second
bandwidth; a second multiplier for multiplying the frequency error
by the phase error and detecting a frequency/phase error; and a
second integrator for accumulating power of the pilot signal
component outputted from the second code detector, and generating a
lock signal to the comparing part if the accumulated power of the
pilot signal component reaches a preset pilot power threshold
value.
6. The carrier recovery apparatus of claim 5, wherein the pilot
power threshold value of the first integrator is greater than that
of the second integrator.
7. The carrier recovery apparatus of claim 4, wherein the comparing
part compares a new first threshold value (lock1) generated from
the first band pilot signal and frequency/phase error detecting
part with a new second threshold value (lock2) generated from the
second band pilot signal and frequency/phase error detecting part,
and outputs the selection signal for selecting one of the output
results of the first and second pilot signal and frequency/phase
detecting parts.
8. The carrier recovery apparatus of claim 7, wherein the comparing
part generates the selection signal for selecting the output result
of the first frequency/phase error detecting part if the first
threshold value (lock1) is activated earlier than the second
threshold value (lock2), and the comparing part generates the
selection signal for selecting the output result of the second
frequency/phase error detecting part if the second threshold value
(lock2) is activated earlier than the first threshold value
(lock1).
9. A carrier recovery apparatus comprising: a complex multiplier
for multiplying a digitalized passband signal by an oscillation
frequency of an oscillator and outputting a recovered carrier wave
of a baseband signal; a first frequency/phase error detecting part
for outputting a frequency/phase error component of a first
bandwidth, the first bandwidth being a bandwidth of an LPF for
extracting a typical pilot signal contained in the baseband signal
outputted from the complex multiplier; a second frequency/phase
error detecting part for outputting a frequency/phase error
component of a second bandwidth among the baseband signals
outputted from the complex multiplier, the second bandwidth being
narrower than the first bandwidth; a pilot power comparing part for
comparing a pilot power of the baseband signal with a preset
threshold value and outputting a selection signal for selecting one
of output results of the first and second frequency/phase detecting
parts; a selecting part for selecting one of the frequency/phase
error components outputted from the first and second
frequency/phase error detecting parts, based on the selection
signal of the comparing part; a loop filter for removing an RF
component contained in the selected frequency/phase error
component; and an oscillator for changing an oscillation frequency
according to the frequency/phase error component whose RF component
is removed.
10. The carrier recovery apparatus of claim 9, wherein the first
frequency/phase error detecting part includes: a first LPF, a first
delay unit and a first code detector, which are configured to form
a loop for receiving a baseband I signal from the complex
multiplier and detecting the frequency error component of the first
bandwidth; a second LPF configured to form a loop for receiving a
baseband Q signal from the complex multiplier and detecting a phase
error of the first bandwidth; and a first multiplier for
multiplying the frequency error by the phase error and detecting a
frequency/phase error, wherein the second frequency/phase error
detecting part includes: a first LPF, a second delay unit and a
second code detector, which are configured to form a loop for
receiving the baseband I signal from the complex multiplier and
detecting the frequency error component of the second bandwidth; a
second LPF configured to form a loop for receiving the baseband Q
signal from the complex multiplier and detecting a phase error of
the second bandwidth; and a second multiplier for multiplying the
frequency error by the phase error and detecting a frequency/phase
error.
11. The carrier recovery apparatus of claim 9, wherein the pilot
power comparing part includes: an LPF for filtering a pilot signal
from the baseband I signal outputted from the complex multiplier; a
power calculator for calculating a power of the filtered pilot
signal; and a comparator for comparing the power of the filtered
pilot signal with a preset threshold value and generating a control
signal for selecting one of the output results of the first and
second frequency/phase error detecting parts.
12. The carrier recovery apparatus of claim 11, wherein the
comparator generates the control signal for selecting the output
result of the first frequency/phase error detecting part if the
power of the pilot signal is greater than a preset threshold value,
and the comparator generates the control signal for selecting the
output result of the second frequency/phase error detecting part if
the power of the pilot signal is less than the preset threshold
value.
13. The carrier recovery apparatus of claim 9, wherein the pilot
power comparing part compares a new first threshold value (lock1)
generated from the first frequency/phase error detecting part with
a new second threshold value (lock2) generated from the second
frequency/phase error detecting part, and outputs the selection
signal for selecting one of the output results of the first and
second pilot signal and frequency/phase detecting parts.
14. A carrier recovery apparatus comprising: a complex multiplier
for multiplying a digitalized passband signal by an oscillation
frequency of an oscillator and outputting a recovered carrier wave
of a baseband signal; a first band signal filtering part for
outputting I and Q signal components of a first bandwidth, the
first bandwidth being a bandwidth of an LPF for extracting a
typical pilot signal contained in the baseband signal outputted
from the complex multiplier; a second band signal filtering part
for outputting I and Q signal components of a second bandwidth
among the baseband signals outputted from the complex multiplier,
the second bandwidth being narrower than the first bandwidth; a
selecting part for receiving the I and Q signal components from the
first and second band signal filtering parts and selecting one I
and Q signal component among the I and Q signal components
outputted from the first and second band signal filtering parts; a
power calculating part for calculating a pilot signal power of a
baseband I signal passing through the first band signal filtering
part, the baseband I signal being outputted from the selecting
part; a comparing part for comparing the calculated pilot signal
power with a preset threshold value and generating a control signal
for selecting the I and Q signal components outputted from one of
the first and second band signal filtering parts; a frequency/phase
error detecting part for detecting a frequency/phase error
component of the I and Q signals outputted from the selecting part;
a loop filter for removing an RF component contained in the
frequency/phase error component outputted from the frequency/phase
error detecting part; and an oscillator for changing an oscillation
frequency according to the frequency/phase error component whose RF
component is removed.
15. The carrier recovery apparatus of claim 14, wherein the
frequency/phase error detecting part includes: a delay unit and a
code detector for detecting a frequency error of the I signal from
the I and Q signals outputted from the selecting part; and a
multiplier for multiplying the frequency error outputted from the
code detector by the phase error contained in the Q signal, and
outputting a frequency/phase error.
16. A VSB (vestigial sideband) receiver for use in a digital TV
receiver for demodulating a passband analog signal into a baseband
digital signal, the VSB receiver comprising: a digital processing
part for selecting a desired channel frequency through an antenna,
converting the channel frequency into an intermediate frequency,
and digitalizing the channel frequency by passing a predetermined
band of the intermediate frequency; a carrier recovery part for
comparing a power value of an output signal of an LPF, which
removes a signal unnecessary for a carrier recovery among the
digitalized passband signals, with a preset reference or threshold
value, and recovering a baseband carrier wave by changing power of
a pilot component of the digitalized passband signal according to
the comparison result; a clock demodulation part for removing the
pilot signal from the baseband signal and extracting a
synchronizing signal; a noise removing part for removing a linear
noise and a residual phase jitter of the baseband signal by using
the synchronizing signal; and a decoding part for decoding the
baseband signal whose noise is removed.
17. The VSB receiver of claim 16, wherein the clock demodulation
part includes a DC limiter for removing the pilot signal and a
synchronizing part for extracting the synchronizing signal from the
signal whose pilot signal is removed; the noise removing part
includes a channel equalizer for removing a linear noise from the
signal whose pilot signal is removed, and a phase tracking unit for
removing a residual phase jitter from the signal whose linear noise
is removed; and the decoding part includes an FEC unit for decoding
the signal the signal whose residual phase jitter is removed.
18. A carrier recovery apparatus comprising: a complex multiplier
for multiplying a digitalized passband signal by an oscillation
frequency of a frequency phase locked loop (FPLL) and outputting a
recovered carrier wave of a baseband signal; the FPLL for filtering
a pilot signal from the baseband signal, locking a frequency and
phase of the baseband signal by using the filtered pilot signal,
and generating the oscillation frequency; and a gain control part
for comparing a power value of the baseband signal inputted to the
FPLL with a preset reference or threshold value, adjusting a power
of the pilot signal contained in the baseband signal outputted from
the complex multiplier and outputting the adjusted pilot signal to
the FPLL.
19. The carrier recovery apparatus of claim 18, wherein the gain
control part includes: a power calculator for calculating a power
of the baseband signal of the complex multiplier from a signal
where data component unnecessary in the carrier recovery is removed
among the baseband signals inputted to the FPLL; a comparator for
comparing the calculated power value with a preset reference or
threshold value; and a gain controller configured between the
complex multiplier and the FPLL, for adjusting power of the pilot
signal by controlling gain of the baseband signal outputted from
the complex multiplier, based on the output result of the
comparator, and outputting the recovered carrier wave.
20. The carrier recovery apparatus of claim 19, wherein the complex
multiplier outputs baseband I and Q signals by multiplying the
oscillation frequency by passband I and Q signals if the
digitalized passband signal is inputted as baseband I and Q signals
having a phase difference of 90.degree., and the gain controller
includes first and second gain controller for controlling gains of
the baseband I and Q signals.
21. The carrier recovery apparatus of claim 19, wherein the FPLL
includes: a frequency locked loop (FLL) for removing unnecessary
data component from the baseband I signal passing through the gain
controller and for locking a frequency, the FLL being configured
with a first LPF, a delay unit, a code detector, a multiplier, a
loop filter and a frequency oscillator; and a phase locked loop
(PLL) for removing unnecessary data component from the baseband Q
signal and for locking a phase, the PLL being configured with a
second LPF, the multiplier, the loop filter and the frequency
oscillator.
22. The carrier recovery apparatus of claim 19, wherein the power
calculator calculates power of the baseband I signal passing
through the first LPF.
23. The carrier recovery apparatus of claim 18, wherein the gain
control part includes: a power calculator for calculating a power
of the baseband signal of the complex multiplier from a signal
where data component unnecessary in the carrier recovery is removed
among the baseband signals inputted to the FPLL; a comparator for
comparing the calculated power value with a preset reference or
threshold value; and a gain controller configured between the a
frequency/phase error detector of the FPLL and a loop filter, for
adjusting power of the pilot signal by controlling gain of the
baseband signal outputted from the frequency/phase error detector,
based on the output result of the comparator, and outputting the
adjusted pilot signal to the loop filter.
24. A carrier recovery apparatus comprising: a complex multiplier
for multiplying a digitalized passband signal by an oscillation
frequency of an oscillator and outputting a recovered carrier wave
of a baseband signal; a first band signal filtering part for
outputting I and Q signal components of a first bandwidth, the
first bandwidth being a bandwidth of an LPF for extracting a
typical pilot signal contained in the baseband signal outputted
from the complex multiplier; a second band signal filtering part
for outputting I and Q signal components of a second bandwidth
among the baseband signals outputted from the complex multiplier,
the second bandwidth being narrower than the first bandwidth; a
selecting part for receiving the I and Q signal components from the
first and second band signal filtering parts and selecting one I
and Q signal component among the I and Q signal components
outputted from the first and second band signal filtering parts; a
power calculating part for calculating a pilot signal power of a
baseband I signal passing through the first band signal filtering
part, the baseband I signal being outputted from the selecting
part; a frequency/phase error detecting part for detecting a
frequency/phase error component of the I and Q signals outputted
from the selecting part; a gain control part for controlling a gain
of the frequency/phase error component outputted from the
frequency/phase error detecting part; a comparing part for
comparing the calculated pilot signal power with a preset threshold
value and generating a control signal for selecting the I and Q
signal components outputted from one of the first and second band
signal filtering parts, and generating a control signal for
controlling the gain of the gain control part according to the
pilot signal power; a loop filter for removing an RF component
contained in the frequency/phase error component outputted from the
gain control part; and an oscillator for changing an oscillation
frequency according to the frequency/phase error component whose RF
component is removed.
25. The carrier recovery apparatus of claim 24, wherein the
frequency/phase error detecting part includes: a delay unit and a
code detector for detecting a frequency error of the I signal from
the I and Q signals outputted from the selecting part; and a
multiplier for multiplying the frequency error outputted from the
code detector by the phase error contained in the Q signal, and
outputting a frequency/phase error.
26. The carrier recovery apparatus of claim 24, wherein the carrier
recovery apparatus normalizes the gain of the gain control part so
as to correspond to the pilot signal power calculated by the power
calculating part.
Description
[0001] This application claims the benefit of the Korean
Application Nos. 10-2003-0086336, filed on Dec. 1, 2003, and
10-2003-0094592, filed on Dec. 22, 2003 which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a digital TV, and more
particularly, to a VSB receiver and a carrier recovery apparatus
thereof, in which a carrier is recovered using a VSB modulated
signal.
[0004] 2. Discussion of the Related Art
[0005] A vestigial sideband (VSB) system of Grand Alliance is
adopted as the standard for a transmission system of digital TV
(e.g., HDTV) in the United States and Korea. In the VSB system,
when a signal is amplitude-modulated, upper and lower sidebands are
generated based on a carrier wave. At this point, when one of the
two sidebands is greatly reduced, the other sideband is modulated.
That is, only one sideband spectrum of a baseband signal is removed
to a passband and then transmitted, such that the VSB modulation is
more efficient in the use of bandwidth.
[0006] In the VSB modulation, if a DC spectrum of a baseband signal
is removed to a passband, the DC spectrum is converted to a tone
spectrum. This signal is called a pilot signal. That is, when a
broadcasting station performs the VSB modulation, the pilot signal
is carried and transmitted together via air so that a receiver can
correctly demodulate the signal.
[0007] FIG. 1 is a schematic block diagram of a general digital TV
transmitter. Referring to FIG. 1, a randomizer 101 randomly outputs
an input data to a Read-Solomon (RS) encoder 102. The RS encoder
102 performs an RS encoding of the randomly inputted data for inner
and outer channel coding and adds a parity code of 20 bytes to
outputs the resulting signal to an interleaver 103.
[0008] The interleaver 103 interleaves the RS encoded data
according to a preset regulation and outputs the interleaved data
to a trellis encoder 104. The trellis encoder 104 converts the
interleaved data into a symbol in byte for a trellis coding and
outputs it to a multiplexer 105.
[0009] The multiplexer 105 performs a multiplexing of a segment
synchronizing signal and a field synchronizing signal to a trellis
coded symbol sequence per segment and frame to thereby form a
frame, and then outputs the frame to a pilot insertion part 106.
The pilot insertion part 106 inserts a pilot signal of a DC value
into the framed transmission symbol and outputs to a VSB modulation
part 107.
[0010] The VSB modulation part 107 modulates the symbol sequence
having the pilot signal inserted thereinto in the VSB system and
outputs the modulated symbol sequence to an RF up-converter 108.
The RF up-converter 108 converts the VSB signal of the modulated
baseband into an RF passband signal so as to effectively transmit
the signal via an antenna.
[0011] FIG. 2 is a block diagram of the VSB modulation part of the
digital TV transmitter shown in FIG. 1.
[0012] Referring to FIG. 2, a channel encoder 201 is configured
with the randomizer 101, the RS encoder 102, the interleaver 103,
the trellis encoder 104, the multiplexer 105, the pilot insertion
part 106, and the VSB modulation part 107 includes a complex filter
202 and an intermediate frequency (IF) modulator 203. A signal
passes through the channel encoder 201 and the VSB modulation part
107. First, for the VSB modulation, the signal passing through the
channel encoder 201 passes through the complex filter 202. At this
point, if the encoded digital signal passes through the complex
filter 202, a Hilbert transformer and an SRC transforms the shapes
of frequencies of I and Q signals such that the I and Q signals can
be VSB-modulated.
[0013] The I and Q signals as the output of the complex filter 202
are IF-modulated at the IF modulator 203 and then subtracted at a
subtracter 204, resulting in a VSB IF signal of a required
bandwidth (6 MHz). In order to transmit the VSB IF signal via radio
wave, the VSB IF signal is converted into an RF passband signal by
the RF up-converter 205 and the RF baseband signal is transmitted
via the antenna.
[0014] FIG. 3 is a block diagram of a general digital TV receiver
based on the ATSC standard.
[0015] In the digital TV receiver, a passband signal of a specific
channel is extracted by a tuner 302 and a carrier wave is recovered
using a pilot signal inserted into a sideband. Then, a transmission
symbol is extracted from the recovered baseband signal by a symbol
timing recovery and a channel compensation.
[0016] Referring to FIG. 3, the digital TV receiver includes: a
tuner 302 for selecting a desired channel frequency from the RF
signal received through an antenna and primarily converting the VSB
signal from the RF band to an IF band; a surface acoustic wave
(SAW) filter 303 for passing a predetermined band of the IF signal
outputted from the tuner 302; an IF processing part 304 for
secondarily converts an output signal of the tuner 302 into an
analog signal; an analog-to-digital converter (ADC) 305 for
converting the analog signal into a digital signal; a carrier
recovery part 306 for converting the digital signal into a baseband
signal; a DC limiter 307 for removing a pilot signal from an output
signal of the carrier recovery part 306; a synchronizing part 308
for extracting a synchronizing signal from an output signal of the
DC limiter 307 and recovering a symbol timing; a channel equalizer
309 for removing a linear noise from the signal whose DC component
is removed; a phase tracking part 310 for removing a residual phase
jitter from the signal whose linear noise is removed; and an FEC
part for decoding the signal, which is an operation opposite to the
digital channel coding of the transmitter.
[0017] The tuner 302, the SAW filter 303 and the IF processing part
304 can be called an analog processing part, and the ADC 305 and
the analog processing part can be called a digital processing part.
Also, the DC limiter 307 and the synchronizing part 308 can be
called a clock demodulation part 312, and the channel equalizer 309
and the phase tracking part 310 can be called a noise removing
part.
[0018] That is, if a VBS-modulated RF signal is received through
the antenna 301, the tuner 302 selects a desired channel frequency
by using a heterodyne modulation system and then the VSB signal of
the RF band carried on the channel frequency is lowered to a fixed
IF band (generally, 44 MHz or 43.75 MHz) and signals of the other
channels are properly filtered.
[0019] An output signal of the tuner 302 passes through the SAW
filter 301, which removes signals of undesired bands and noise
signals and serves as an analog matching filter.
[0020] For example, a digital broadcasting signal has all
information within a band from the IF band of 44 MHz to a frequency
band of 6 MHz, so that the SAW filter 303 removes all sections from
the output signal of the tuner 302, except the band of 6 MHz in
which information exists, and then outputs the remaining band
signal to the IF processing part 304.
[0021] The IF processing part 304 converts the signal into an
analog signal, and the ADC 305 converts the analog signal into a
digital signal.
[0022] The passband signal converted into the digital signal is
demodulated into a baseband signal by the carrier recovery part
306. In the baseband signal, a frequency of the pilot signal
inserted for the carrier demodulation at the transmitter changes to
0 Hz, which is a DC component.
[0023] Since the DC component finished its role, the DC component
is removed by the DC limiter 307.
[0024] Information of a synchronizing signal section is extracted
by the synchronizing part 308. The information of the synchronizing
signal section is used in the channel equalizer 309, the phase
tracking part 310 and the FEC part 311.
[0025] The signal whose DC component is removed passes through the
channel equalizer 309 to remove linear noises existing in the
transport channel and the analog processing part of the receiver.
Then, the signal passes through the phase tracking part 310 for
removing the residual phase jitter and then it is decoded by the
FEC part 311. If this process is finished, the digital TV receiver
completes its function, and the transport stream equal to the
signal inputted from the transmitter to the receiver is transmitted
to a video/audio signal processing part (not shown).
[0026] FIG. 4 is a block diagram of the carrier recovery part of
the digital TV receiver shown in FIG. 3.
[0027] In FIG. 4, the carrier recovery part 306 is implemented with
a frequency phase locked loop (FPLL) proposed in the ATSC
standard.
[0028] Referring to FIG. 4, if the passband analog signal is
converted into the digital signal, a Hilbert transformer 402 shifts
the signal by 90.degree. such that the digital signal is
transformed into a Q signal of an imaginary component. A delay unit
401 delays the digital signal by a predetermined time when the
digital signal is transformed into the Q signal at the Hilbert
transformer 402, and then outputs an I signal of a real component.
A complex multiplier 403 multiplies the I and Q signals by an
output signal of a voltage controlled oscillator (VCO) 410 to
output a baseband I signal and a baseband Q signal. An FPLL
includes a frequency phase locked loop (FLL) and a phase locked
loop (PLL). The FLL includes an I signal low pass filter (LPF) 404,
a delay unit 406, a code detector 407, a multiplier 408, a loop
filter 409, and a VCO (or a numerically controlled oscillator
(NCO)) 410. The FLL locks a frequency of the baseband I signal
outputted from the complex multiplier 403. The PLL includes a Q
signal LPF 405, the multiplexer 408, the loop filter 409 and the
VCO 410. The PLL locks a frequency of the baseband Q signal
outputted from the complex multiplier 403.
[0029] Here, the I signal LPF 404, the delay unit 406 and the code
detector 407 detect a frequency error, and the Q signal LPF detects
a phase error from the detected frequency error. Then, the
multiplier 408 multiplies the frequency error and the phase error
to thereby obtain final frequency and phase error components (the
controlled voltage).
[0030] The loop filter 409 removes RF components from the frequency
and phase error components, and the VCO 410 converts an oscillation
frequency according to the frequency and phase error components
(the controlled voltage).
[0031] That is, the loop filter 409 filters only the baseband
signal and the VCO 410 outputs the oscillation frequency varying
according to the output signal of the loop filter 409. A beat
frequency is removed by changing the frequency and phase of the
carrier wave according to the varied oscillation frequency
outputted from the VCO 410.
[0032] In the carrier recovery part 306, the I signal and the Q
signal are demodulated and the frequency and phase are locked by
separating the phase from the output signal of the SAW filter 303.
Here, the center frequency of the VCO 410 is fixed to an
intermediate frequency (for example, 46.690559 MHz) and the complex
multiplier 403 multiplies the output of the VCO 410 and the output
of the SAW filter 303 to thereby generate a baseband I channel
signal i(t) and a baseband Q channel signal q(t).
[0033] At this point, the receiver can operate normally when the
frequency of the pilot signal accurately is at the intermediate
frequency (for example, 46.690559 MHz) at the output of the SAW
filter 303. However, in many cases, the frequency of the pilot
signal is not 46.690559 MHz.
[0034] Meanwhile, the output frequency of the VCO 410 is fixed to
46.690559 MHz. Thus, when the output frequency of the pilot signal
is not 46.690559 MHz, there exists a beat frequency corresponding
to a difference of two frequencies outputted from the complex
multiplier 403. The FPLL is used to remove the beat frequency. That
is, the frequency and phase of the carrier wave are changed due to
the variation in the oscillation frequency of the VCO 410 and thus
the beat frequency is removed. Accordingly, an object of the FPLL
is to find a direction and magnitude of the movement of the
oscillation frequency of the VCO 410.
[0035] The FPLL has a combination of a frequency locking look and a
phase locking loop.
[0036] In FIG. 4, the frequency locking loop is configured with an
auto frequency control filter (AFC), the code detector 407, the
multiplier 408, the loop filter 409, the VCO 410 and the complex
multiplier 403, and the phase locking loop is configured with the
LPF 405, the multiplier 408, the loop filter 409, the VCO 410 and
the complex multiplier 403.
[0037] FIGS. 5A to 5C are diagrams explaining a characteristic of
the output signal of the complex multiplier and FIGS. 6A to 6C are
diagrams explaining another characteristic of the output signal of
the complex multiplier.
[0038] FIG. 5A shows a spectrum characteristic of the baseband I
signal when the pilot signal is stably received, and FIGS. 5B and
5C show spectrum characteristics when the pilot signal component
gets weaker while passing through the channel and therefore its
position cannot be correctly found on the spectrum.
[0039] In the case of the FPLL that is dependent on the pilot, data
component except the pilot component does not provide information
necessary for the carrier recovery and also causes a jitter due to
data after the carrier recovery. For these reasons, as shown in
FIG. 4, the LPF is used to extract the pilot component from the
received data.
[0040] When the pilot signal is weak due to the channel, it is
preferable to use an LPF having a narrow bandwidth to extract the
pilot signal from the data. However, if a carrier frequency offset
exists due to the channel in such a state that the pilot signal is
not weak, it is preferable to use an LPF having a wide bandwidth,
as shown in FIGS. 5B and 5C. Meanwhile, if the component of the
pilot signal is severely weak, even the LPF having the wide
bandwidth cannot easily extract the pilot component.
[0041] FIG. 6A shows a spectrum characteristic of the baseband I
signal when the pilot signal is stably received, and FIGS. 6B and
6C shows spectrum characteristics when the frequency offset exists
in such a state that the power of the pilot signal is not weak and
thus its position cannot be correctly found on the spectrum. As
shown in FIGS. 6A to 6C, in case where the LPF having a narrow
bandwidth is used, if the pilot signal is out of the narrow
bandwidth, it is difficult to extract the pilot component.
[0042] According to the prior art, as described above, the LPF
having the wide bandwidth is used to extract the pilot signal.
Thus, when the frequency offset exists, no problem occurs. However,
if the pilot signal is damaged due to the channel, power of the I
signal from the complex multiplier becomes very weak near the DC.
Therefore, in the system which performs the carrier recovery based
on the pilot signal, its performance is degraded and thus the
carrier cannot be recovered. If the LPF having the narrow bandwidth
is simply used to extract the pilot signal, it is impossible to
solve the problems occurring when the carrier frequency offset
exists.
SUMMARY OF THE INVENTION
[0043] Accordingly, the present invention is directed to a VSB
receiver and a carrier recovery apparatus thereof that
substantially obviates one or more problems due to limitations and
disadvantages of the related art.
[0044] An object of the present invention is to provide a VSB
receiver and a carrier recovery apparatus thereof, in which a pilot
signal component can be easily extracted by automatically
controlling a bandwidth of a filter for filtering a pilot signal
component passing through a transmission channel when a carrier
wave is recovered using a VSB modulated signal.
[0045] Additional advantages, objects, and features of the
invention will be set forth in part in the description which
follows and in part will become apparent to those having ordinary
skill in the art upon examination of the following or may be
learned from practice of the invention. The objectives and other
advantages of the invention may be realized and attained by the
structure particularly pointed out in the written description and
claims hereof as well as the appended drawings.
[0046] To achieve these objects and other advantages and in
accordance with the purpose of the invention, as embodied and
broadly described herein, a VSB (vestigial sideband) receiver for
use in a digital TV receiver for demodulating a passband analog
signal into a baseband digital signal, the VSB receiver including:
a digital processing part for selecting a desired channel frequency
through an antenna, converting the channel frequency into an
intermediate frequency, and digitalizing the channel frequency by
passing a predetermined band of the intermediate frequency; a
carrier recovery part for extracting pilot signals by using a first
LPF having a first bandwidth and a second LPF having a second
bandwidth, and recovering a baseband carrier wave signal from a
passband signal by using one of the extracted pilot signals; a
clock demodulation part for removing the pilot signal from the
baseband carrier wave signal and extracting a synchronizing signal;
a noise removing part for removing a linear noise and a residual
phase jitter of the baseband signal by using the synchronizing
signal; and a decoding part for decoding the baseband signal whose
noise is removed.
[0047] The carrier recovery part may further include: a comparator
for comparing powers of pilot components passing through the first
and second LPFs; a selector for selecting one of the pilot
components extracted from the first and second LPFs according to
the comparison result of the comparator.
[0048] The comparator compares a first threshold value (lock1) and
a second threshold value (lock2), the first threshold value (lock1)
being generated from a first carrier recovery part using the first
LPF, the second threshold value (lock2) being generated from a
second carrier recovery part using the second LPF.
[0049] The present invention provides a carrier recovery apparatus
including: a complex multiplier for multiplying a digitalized
passband signal by an oscillation frequency of an oscillator and
outputting a recovered carrier wave of a baseband signal; a first
band pilot signal and frequency/phase error detecting part for
outputting a pilot signal component and a frequency/phase error
component of a first bandwidth, the first bandwidth being a
bandwidth of an LPF for extracting a typical pilot signal contained
in the baseband signal outputted from the complex multiplier; a
second band pilot signal and frequency/phase error detecting part
for outputting a pilot signal component and a frequency/phase error
component of a second bandwidth among the baseband signals
outputted from the complex multiplier, the second bandwidth being
narrower than the first bandwidth; a comparing part for comparing
the pilot signal components outputted from the first and second
band pilot signal and frequency/phase error detecting parts, and
outputting a selection signal for selecting one of output results
of the first and second pilot signal and frequency/phase detecting
parts; a selecting part for selecting one of the frequency/phase
error components outputted from the first and second band pilot
signal and frequency/phase error detecting parts, based on the
selection signal of the comparing part; a loop filter for removing
an RF component contained in the selected frequency/phase error
component; and an oscillator for changing an oscillation frequency
according to the frequency/phase error component whose RF component
is removed.
[0050] The first band pilot signal and frequency/phase error
detecting part may include: a first LPF, a first delay unit and a
first code detector, which are configured to form a loop for
receiving a baseband I signal from the complex multiplier and
detecting the pilot signal component and the frequency error
component of the first bandwidth; a second LPF configured to form a
loop for receiving a baseband Q signal from the complex multiplier
and detecting a phase error of the first bandwidth; a first
multiplier for multiplying the frequency error by the phase error
and detecting a frequency/phase error; and a first integrator for
accumulating power of the pilot signal component outputted from the
first code detector, and generating a lock signal to the comparing
part if the accumulated power of the pilot signal component reaches
a preset pilot power threshold value, wherein the second band pilot
signal and frequency/phase error detecting part includes: a first
LPF, a second delay unit and a second code detector, which are
configured to form a loop for receiving the baseband I signal from
the complex multiplier and detecting the pilot signal component and
the frequency error component of the second bandwidth; a second LPF
configured to form a loop for receiving the baseband Q signal from
the complex multiplier and detecting a phase error of the second
bandwidth; a second multiplier for multiplying the frequency error
by the phase error and detecting a frequency/phase error; and a
second integrator for accumulating power of the pilot signal
component outputted from the second code detector, and generating a
lock signal to the comparing part if the accumulated power of the
pilot signal component reaches a preset pilot power threshold
value.
[0051] The pilot power threshold value of the first integrator is
greater than that of the second integrator.
[0052] The comparing part compares a new first threshold value
(lock1) generated from the first band pilot signal and
frequency/phase error detecting part with a new second threshold
value (lock2) generated from the second band pilot signal and
frequency/phase error detecting part, and outputs the selection
signal for selecting one of the output results of the first and
second pilot signal and frequency/phase detecting parts.
[0053] The comparing part generates the selection signal for
selecting the output result of the first frequency/phase error
detecting part if the first threshold value (lock1) is activated
earlier than the second threshold value (lock2), and the comparing
part generates the selection signal for selecting the output result
of the second frequency/phase error detecting part if the second
threshold value (lock2) is activated earlier than the first
threshold value (lock1).
[0054] The present invention provides a carrier recovery apparatus
including: a complex multiplier for multiplying a digitalized
passband signal by an oscillation frequency of an oscillator and
outputting a recovered carrier wave of a baseband signal; a first
frequency/phase error detecting part for outputting a
frequency/phase error component of a first bandwidth, the first
bandwidth being a bandwidth of an LPF for extracting a typical
pilot signal contained in the baseband signal outputted from the
complex multiplier; a second frequency/phase error detecting part
for outputting a frequency/phase error component of a second
bandwidth among the baseband signals outputted from the complex
multiplier, the second bandwidth being narrower than the first
bandwidth; a pilot power comparing part for comparing a pilot power
of the baseband signal with a preset threshold value and outputting
a selection signal for selecting one of output results of the first
and second frequency/phase detecting parts; a selecting part for
selecting one of the frequency/phase error components outputted
from the first and second frequency/phase error detecting parts,
based on the selection signal of the comparing part; a loop filter
for removing an RF component contained in the selected
frequency/phase error component; and an oscillator for changing an
oscillation frequency according to the frequency/phase error
component whose RF component is removed.
[0055] The first frequency/phase error detecting part includes: a
first LPF, a first delay unit and a first code detector, which are
configured to form a loop for receiving a baseband I signal from
the complex multiplier and detecting the frequency error component
of the first bandwidth; a second LPF configured to form a loop for
receiving a baseband Q signal from the complex multiplier and
detecting a phase error of the first bandwidth; and a first
multiplier for multiplying the frequency error by the phase error
and detecting a frequency/phase error, wherein the second
frequency/phase error detecting part includes: a first LPF, a
second delay unit and a second code detector, which are configured
to form a loop for receiving the baseband I signal from the complex
multiplier and detecting the frequency error component of the
second bandwidth; a second LPF configured to form a loop for
receiving the baseband Q signal from the complex multiplier and
detecting a phase error of the second bandwidth; and a second
multiplier for multiplying the frequency error by the phase error
and detecting a frequency/phase error.
[0056] The pilot power comparing part includes: an LPF for
filtering a pilot signal from the baseband I signal outputted from
the complex multiplier; a power calculator for calculating a power
of the filtered pilot signal; and a comparator for comparing the
power of the filtered pilot signal with a preset threshold value
and generating a control signal for selecting one of the output
results of the first and second frequency/phase error detecting
parts.
[0057] The comparator generates the control signal for selecting
the output result of the first frequency/phase error detecting part
if the power of the pilot signal is greater than a preset threshold
value, and the comparator generates the control signal for
selecting the output result of the second frequency/phase error
detecting part if the power of the pilot signal is less than the
preset threshold value.
[0058] The pilot power comparing part compares a new first
threshold value (lock1) generated from the first frequency/phase
error detecting part with a new second threshold value (lock2)
generated from the second frequency/phase error detecting part, and
outputs the selection signal for selecting one of the output
results of the first and second pilot signal and frequency/phase
detecting parts.
[0059] The present invention provides a carrier recovery apparatus
including: a complex multiplier for multiplying a digitalized
passband signal by an oscillation frequency of an oscillator and
outputting a recovered carrier wave of a baseband signal; a first
band signal filtering part for outputting I and Q signal components
of a first bandwidth, the first bandwidth being a bandwidth of an
LPF for extracting a typical pilot signal contained in the baseband
signal outputted from the complex multiplier; a second band signal
filtering part for outputting I and Q signal components of a second
bandwidth among the baseband signals outputted from the complex
multiplier, the second bandwidth being narrower than the first
bandwidth; a selecting part for receiving the I and Q signal
components from the first and second band signal filtering parts
and selecting one I and Q signal component among the I and Q signal
components outputted from the first and second band signal
filtering parts; a power calculating part for calculating a pilot
signal power of a baseband I signal passing through the first band
signal filtering part, the baseband I signal being outputted from
the selecting part; a comparing part for comparing the calculated
pilot signal power with a preset threshold value and generating a
control signal for selecting the I and Q signal components
outputted from one of the first and second band signal filtering
parts; a frequency/phase error detecting part for detecting a
frequency/phase error component of the I and Q signals outputted
from the selecting part; a loop filter for removing an RF component
contained in the frequency/phase error component outputted from the
frequency/phase error detecting part; and an oscillator for
changing an oscillation frequency according to the frequency/phase
error component whose RF component is removed.
[0060] The frequency/phase error detecting part includes: a delay
unit and a code detector for detecting a frequency error of the I
signal from the I and Q signals outputted from the selecting part;
and a multiplier for multiplying the frequency error outputted from
the code detector by the phase error contained in the Q signal, and
outputting a frequency/phase error.
[0061] The present invention provides a VSB (vestigial sideband)
receiver for use in a digital TV receiver for demodulating a
passband analog signal into a baseband digital signal, the VSB
receiver including: a digital processing part for selecting a
desired channel frequency through an antenna, converting the
channel frequency into an intermediate frequency, and digitalizing
the channel frequency by passing a predetermined band of the
intermediate frequency; a carrier recovery part for comparing a
power value of an output signal of an LPF, which removes a signal
unnecessary for a carrier recovery among the digitalized passband
signals, with a preset reference or threshold value, and recovering
a baseband carrier wave by changing power of a pilot component of
the digitalized passband signal according to the comparison result;
a clock demodulation part for removing the pilot signal from the
baseband signal and extracting a synchronizing signal; a noise
removing part for removing a linear noise and a residual phase
jitter of the baseband signal by using the synchronizing signal;
and a decoding part for decoding the baseband signal whose noise is
removed.
[0062] The clock demodulation part includes a DC limiter for
removing the pilot signal and a synchronizing part for extracting
the synchronizing signal from the signal whose pilot signal is
removed; the noise removing part includes a channel equalizer for
removing a linear noise from the signal whose pilot signal is
removed, and a phase tracking unit for removing a residual phase
jitter from the signal whose linear noise is removed; and the
decoding part includes an FEC unit for decoding the signal the
signal whose residual phase jitter is removed.
[0063] The present invention provides a carrier recovery apparatus
includes: a complex multiplier for multiplying a digitalized
passband signal by an oscillation frequency of a frequency phase
locked loop (FPLL) and outputting a recovered carrier wave of a
baseband signal; the FPLL for filtering a pilot signal from the
baseband signal, locking a frequency and phase of the baseband
signal by using the filtered pilot signal, and generating the
oscillation frequency; and a gain control part for comparing a
power value of the baseband signal inputted to the FPLL with a
preset reference or threshold value, adjusting a power of the pilot
signal contained in the baseband signal outputted from the complex
multiplier and outputting the adjusted pilot signal to the
FPLL.
[0064] The gain control part includes: a power calculator for
calculating a power of the baseband signal of the complex
multiplier from a signal where data component unnecessary in the
carrier recovery is removed among the baseband signals inputted to
the FPLL; a comparator for comparing the calculated power value
with a preset reference or threshold value; and a gain controller
configured between the complex multiplier and the FPLL, for
adjusting power of the pilot signal by controlling gain of the
baseband signal outputted from the complex multiplier, based on the
output result of the comparator, and outputting the recovered
carrier wave.
[0065] The complex multiplier outputs baseband I and Q signals by
multiplying the oscillation frequency by passband I and Q signals
if the digitalized passband signal is inputted as baseband I and Q
signals having a phase difference of 90.degree., and the gain
controller includes first and second gain controller for
controlling gains of the baseband I and Q signals.
[0066] The FPLL includes: a frequency locked loop (FLL) for
removing unnecessary data component from the baseband I signal
passing through the gain controller and for locking a frequency,
the FLL being configured with a first LPF, a delay unit, a code
detector, a multiplier, a loop filter and a frequency oscillator;
and a phase locked loop (PLL) for removing unnecessary data
component from the baseband Q signal and for locking a phase, the
PLL being configured with a second LPF, the multiplier, the loop
filter and the frequency oscillator.
[0067] The power calculator calculates power of the baseband I
signal passing through the first LPF.
[0068] The gain control part includes: a power calculator for
calculating a power of the baseband signal of the complex
multiplier from a signal where data component unnecessary in the
carrier recovery is removed among the baseband signals inputted to
the FPLL; a comparator for comparing the calculated power value
with a preset reference or threshold value; and a gain controller
configured between the a frequency/phase error detector of the FPLL
and a loop filter, for adjusting power of the pilot signal by
controlling gain of the baseband signal outputted from the
frequency/phase error detector, based on the output result of the
comparator, and outputting the adjusted pilot signal to the loop
filter.
[0069] The present invention provides a carrier recovery apparatus
including: a complex multiplier for multiplying a digitalized
passband signal by an oscillation frequency of an oscillator and
outputting a recovered carrier wave of a baseband signal; a first
band signal filtering part for outputting I and Q signal components
of a first bandwidth, the first bandwidth being a bandwidth of an
LPF for extracting a typical pilot signal contained in the baseband
signal outputted from the complex multiplier; a second band signal
filtering part for outputting I and Q signal components of a second
bandwidth among the baseband signals outputted from the complex
multiplier, the second bandwidth being narrower than the first
bandwidth; a selecting part for receiving the I and Q signal
components from the first and second band signal filtering parts
and selecting one I and Q signal component among the I and Q signal
components outputted from the first and second band signal
filtering parts; a power calculating part for calculating a pilot
signal power of a baseband I signal passing through the first band
signal filtering part, the baseband I signal being outputted from
the selecting part; a frequency/phase error detecting part for
detecting a frequency/phase error component of the I and Q signals
outputted from the selecting part; a gain control part for
controlling a gain of the frequency/phase error component outputted
from the frequency/phase error detecting part; a comparing part for
comparing the calculated pilot signal power with a preset threshold
value and generating a control signal for selecting the I and Q
signal components outputted from one of the first and second band
signal filtering parts, and generating a control signal for
controlling the gain of the gain control part according to the
pilot signal power; a loop filter for removing an RF component
contained in the frequency/phase error component outputted from the
gain control part; and an oscillator for changing an oscillation
frequency according to the frequency/phase error component whose RF
component is removed.
[0070] The frequency/phase error detecting part includes: a delay
unit and a code detector for detecting a frequency error of the I
signal from the I and Q signals outputted from the selecting part;
and a multiplier for multiplying the frequency error outputted from
the code detector by the phase error contained in the Q signal, and
outputting a frequency/phase error.
[0071] The carrier recovery apparatus normalizes the gain of the
gain control part so as to correspond to the pilot signal power
calculated by the power calculating part.
[0072] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0073] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiment(s) of
the invention and together with the description serve to explain
the principle of the invention. In the drawings:
[0074] FIG. 1 is a schematic block diagram of a general digital TV
transmitter;
[0075] FIG. 2 is a block diagram of a VSB modulation part of the
digital TV transmitter shown in FIG. 1;
[0076] FIG. 3 is a block diagram of a general digital TV
receiver;
[0077] FIG. 4 is a block diagram of a carrier recovery part of the
digital TV receiver shown in FIG. 3;
[0078] FIGS. 5A to 5C show characteristics of an output signal of a
complex multiplier shown in FIG. 4;
[0079] FIGS. 6A to 6C show another characteristics of an output
signal of a complex multiplier shown in FIG. 4;
[0080] FIG. 7 is a block diagram of a carrier recovery part of a
digital TV receiver according to a first embodiment of the present
invention;
[0081] FIG. 8 is a block diagram of a carrier recovery part of a
digital TV receiver according to a second embodiment of the present
invention;
[0082] FIG. 9 is a block diagram of a carrier recovery part of a
digital TV receiver according to a third embodiment of the present
invention;
[0083] FIG. 10 is a block diagram of a carrier recovery part of a
digital TV receiver according to a fourth embodiment of the present
invention;
[0084] FIG. 11 is a block diagram of a carrier recovery part of a
digital TV receiver according to a fifth embodiment of the present
invention;
[0085] FIG. 12 is a block diagram of a carrier recovery part of a
digital TV receiver according to a sixth embodiment of the present
invention; and
[0086] FIGS. 13A and 13B shows detection of a pilot signal based on
a bandwidth selected by a carrier recovery part according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0087] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers will be used throughout the drawings to
refer to the same or like parts.
[0088] FIG. 7 is a block diagram of a carrier recovery part of a
digital TV receiver according to a first embodiment of the present
invention.
[0089] Referring to FIG. 7, the carrier recovery part of the
digital TV receiver includes a complex multiplier 701, a first band
pilot signal and frequency/phase error detecting part 718, a second
band pilot signal and frequency/phase error detecting part 719, a
comparing part 712, a selecting part 713, a loop filter 714, and a
VCO (or an NCO) 715.
[0090] The complex multiplier 701 receives an I signal and a Q
signal from a delay unit (not shown) and a Hilbert transformer (not
shown), multiplies the I signal and the Q signals by an output
signal of the VCO 715, and outputs a baseband I signal and a
baseband Q signal (carrier wave). The first band pilot signal and
frequency/phase error detecting part 718 includes first and second
LPFs 702 and 703 having a first bandwidth, a first delay unit 704,
a first code detector 705, a first multiplier 706, and a first
integrator 716. The first band pilot signal and frequency/phase
error detecting part 718 detects a pilot signal component and
frequency/phase error component of a first band among the baseband
I and Q signals outputted from the complex multiplier 701. The
second band pilot signal and frequency/phase error detecting part
719 includes first and second LPFs 707 and 708 having a second
bandwidth narrower than the first bandwidth, a second delay unit
709, a second code detector 710, a second multiplier 711, and a
second integrator 717. The second band pilot signal and
frequency/phase error detecting part 719 detects a pilot signal
component and frequency/phase error component of a second band
among the baseband I and Q signals outputted from the complex
multiplier 701. The comparing part 712 compares the detected pilot
signal components, which are outputted from the first and second
band pilot signal and frequency/phase error detecting parts 718 and
719. The selecting part 713 selectively outputs the frequency/phase
error results, which are respectively outputted from the first and
second band pilot signal and frequency/phase error detecting parts
718 and 719, depending on the comparison result of the comparing
part 712. The loop filter 714 removes an RF component from the
frequency/phase error component, which is outputted from the
selecting part 713. The VCO 715 changes an oscillation frequency
according to the frequency/phase error component whose RF component
is removed.
[0091] In the first to sixth embodiments of the present invention,
pilot signals are detected with respect to a passband signal at a
wide bandwidth and a narrow bandwidth. Thus, when the frequency
offset occurs and when the pilot signal is weak, a suitable
bandwidth is automatically selected, or a gain of the
frequency/phase error information is adjusted.
[0092] A basic structure of the first to sixth embodiments is
similar to that of FIG. 3. However, when the carrier recovery part
recovers the carrier wave, a digital processing part selects a
desired channel frequency through an antenna and digitalizes it by
passing a predetermined band of an intermediate frequency. In this
case, the pilot signals are detected at a wide bandwidth and a
narrow bandwidth. When the frequency offset occurs or when power of
the pilot signal is weak, a fast pilot signal component is detected
to thereby recover the carrier wave.
[0093] In addition, since the clock demodulation part for removing
the pilot signal and extracting the synchronizing signal, the noise
removing part for removing a linear noise and a residual phase
jitter of the baseband signal by using the synchronizing signal,
and the decoding part (for example, the FEC part) for decoding the
baseband signal whose noise is removed have the same structures as
the general TV receiver, a detailed description thereof will be
omitted.
[0094] If the first bandwidth is equal to the bandwidth used to
detect the pilot signal at the conventional carrier recovery part,
it is assumed that the first and second LPFs 707 and 708 of the
second bandwidth have relatively narrow bandwidths (for example,
{fraction (1/2)} to {fraction (1/4)}) than the first and second
LPFs 702 and 703 of the first band. That is, the first bandwidth is
used to extract the pilot signal component when the frequency
offset exists at a wide band, and the second bandwidth is used to
extract the weak pilot signal component at a narrow band.
[0095] Generally, if the frequency is fixed by the FPLL, the pilot
signal is positioned at a DC and the first and second code
detectors 705 and 710 continuously extract and output "1".
[0096] At this point, the pilot signal component passing through
the first LPF 702 of the first band is accumulated at the first
integrator 716 through the first code detector 705, and the pilot
signal component passing through the first LPF 707 of the second
band is accumulated at the second code detector 710 through the
second code detector 710.
[0097] When the accumulated values reach pilot power levels
(threshold) that are set to the respective integrators, the first
and second integrators 716 and 717 generate frequency lock
signals.
[0098] Here, the output values of the first and second integrators
716 and 717 can represent the information on the
convergence/divergence of the frequency locked loop (FLL). In order
to select one of the two loops, the values accumulated at the first
and second integrators 716 and 717 need to be checked by using the
threshold values of the respective integrators 716 and 717, that
is, the threshold value less that the lock value (in the case of
the first integrator 716, it will be referred to as a first
threshold value lock, and in the case of the second integrator 717,
it will be referred to as a second threshold value lock2).
[0099] That is, the first integrator 716 transfers the convergence
state to the comparing part 712 at the loop of the first band pilot
signal and frequency/phase error detecting part 718, and the second
integrator 717 transfers the convergence state to the comparing
part 712 at the loop of the second band pilot signal and
frequency/phase error detecting part 719. In this manner, the
comparing part 712 can fast select a loop suitable for the
convergence from the two loops by applying the first and second
threshold values lock1 and lock2 lower than the original threshold
value (lock).
[0100] If the entire loop includes the FPLL loop configured with
the LPFs 702 and 703 having a wide bandwidth and the FPLL loop
configured with the LPFs 707 and 708 having a narrow bandwidth, the
respective loops generate new lock signals lock1 and lock2
according to new threshold values and the comparing part 712
compares the two new lock values and generates a selection signal
to the selecting part 713 so as to enable the selection of one
loop.
[0101] At this point, by making the loop having a wide bandwidth
satisfy a frequency locking range recommended at the DTV standard
of the ATSC, the comparing part 712 compares the two lock signals
lock1 and lock2. In a general channel situation where the pilot
signal is normally received, a loop having a wide bandwidth is
used. Also, in case where both the loops are locked, the loop
having the wide bandwidth is used for stability of the loop.
[0102] FIG. 13A shows the detection of the pilot signal component
at the first and second LPFs 702 and 703 of the first bandwidth,
and FIG. 13B shows the detection of the pilot signal component at
the first and second LPFs 707 and 708 of the second bandwidth
narrower than the first bandwidth. The output result of the
comparing part 712 can allow the fast selection of the suitable
loop among the output results of the integrators 716 and 717 by
applying the first and second threshold values lock1 and lock2.
Accordingly, if the power of the pilot signal component is greater
than the first threshold value lock1, the pilot signal of the LPF
side having a wide frequency bandwidth is detected such that the
pilot signal detection error is prevented, as shown in FIG. 13A. If
the power of the pilot signal component is greater than the second
threshold value lock2, the pilot signal of the LPF side having a
narrow frequency bandwidth is detected. In this manner, when the
power of the pilot signal is weak, the pilot signal detection error
can be minimized.
[0103] Like this, if the one loop of the first band pilot signal
and frequency/phase error detecting part 718 and the second band
pilot signal and frequency/phase error detecting part 719 is
decided, the selecting part 713 outputs only the frequency/phase
error component (control component) of the decided loop to the loop
filter 714. The loop filter 714 removes RF component contained in
the frequency/phase error component and outputs the resulting
signal to the VCO 715. The VCO 715 changes the oscillation
frequency according to the controlled voltage and outputs to the
complex multiplier 701. At this point, the FPLL is configured with
the pilot signal and frequency/phase error detecting part of the
decided loop, the loop filter 714, and the VCO 715.
[0104] FIG. 8 is a block diagram of a carrier recovery part of a
digital TV receiver according to a second embodiment of the present
invention.
[0105] Referring to FIG. 8, the carrier recovery part of the
digital TV receiver includes a complex multiplier 801, a first
frequency/phase error detecting part 818, a second frequency/phase
error detecting part 819, a pilot power comparing part 820, a
selecting part 815, a loop filter 816, and a VCO 817.
[0106] The complex multiplier 810 receives an I signal and a Q
signal from a delay unit (not shown) and a Hilbert transformer (not
shown), multiplies the I signal and the Q signals by an output
signal of the VCO (or NCO) 817, and outputs a baseband I signal and
a baseband Q signal (carrier wave). The first frequency/phase error
detecting part 818 includes first and second LPFs 802 and 803
having a first bandwidth, a first delay unit 804, a first code
detector 805, and a first multiplier 806. The first frequency/phase
error detecting part 818 detects a first frequency/phase error
component of a first band among the baseband I and Q signals
outputted from the complex multiplier 801. The second
frequency/phase error detecting part 819 includes first and second
LPFs 807 and 808 having a second bandwidth narrower than the first
bandwidth, a second delay unit 809, a second code detector 810 and
a second multiplier 811. The second frequency/phase error detecting
part 819 detects a frequency/phase error component of a second band
among the baseband I and Q signals outputted from the complex
multiplier 801. The pilot power comparing part 820 includes a third
LPF 812, a power calculator 813 and a comparator 814. The pilot
power comparing part 820 extracts a pilot signal from the baseband
I signal, compares power of the pilot signal with a preset
threshold value, and generates a control signal for selecting one
of the results outputted from the first and second frequency/phase
error detecting parts 818 and 819. The selecting part 815
selectively outputs one of the frequency/phase error results
outputted from the first and second frequency/phase error detecting
parts 818 and 819, depending on the comparison result of the
comparing part 820. The loop filter 816 removes an RF component
from the frequency/phase error component, which is outputted from
the selecting part 815. The VCO 715 changes an oscillation
frequency according to the frequency/phase error component whose RF
component is removed.
[0107] The first bandwidth and the second bandwidth of the second
embodiment have the same range as those of the first embodiment.
The third LPF 812 of the pilot power comparing part 820 passes only
the signal of a frequency bandwidth where the pilot signal is
contained among the baseband I signal outputted from the complex
multiplier 801, and the power calculator 813 calculates the power
of the pilot signal and transmits it to the comparing part 814.
[0108] That is, the comparing part 820 compares the power of the
pilot signal with the preset threshold value. If the power of the
pilot signal is greater than the threshold value, the comparing
part 820 generates the control signal for selecting the first
frequency/phase error detecting part 818. If the power of the pilot
signal is less than the threshold value, the comparing part 820
generates the control signal for selecting the second
frequency/phase error detecting part 819.
[0109] The selecting part 815 outputs the frequency/phase error
component (control component) of the decided loop (the first
frequency/phase error detecting parts 818 or the second
frequency/phase error detecting part 819) to the loop filter 816.
The loop filter 816 removes RF component contained in the
frequency/phase error component (control component) and outputs the
resulting signal to the VCO 817. The VCO 817 changes the
oscillation frequency according to the controlled voltage and
outputs to the complex multiplier 801. At this point, the
frequency/phase error detecting part of the decided loop, the loop
filter 816 and the VCO 817 operate as the FPLL.
[0110] FIG. 9 is a block diagram of a carrier recovery part of a
digital TV receiver according to a third embodiment of the present
invention.
[0111] Referring to FIG. 9, the carrier recovery part of the
digital TV receiver includes a complex multiplier 901, a first band
signal filtering part 914, a second band signal filtering part 915,
a selecting part 906, a power calculating part 907, a comparing
part 908, a frequency/phase error detecting part 916, a loop filter
912, and a VCO (or NCO) 913.
[0112] The complex multiplier 810 receives an I signal and a Q
signal from a delay unit (not shown) and a Hilbert transformer (not
shown), multiplies the I signal and the Q signals by an output
signal of the VCO (or NCO) 913, and outputs a baseband I signal and
a baseband Q signal (carrier wave). The first band signal filtering
part 914 includes first and second LPFs 902 and 903 having a first
bandwidth and filters a signal component except the I and Q signal
components of the first band among the baseband signals outputted
from the complex multiplier 901. The second band signal filtering
part 915 includes first and second LPFs 904 and 905 having a second
bandwidth and filters a signal component except the I and Q signal
components of the second band among the baseband signals outputted
from the complex multiplier 901.
[0113] The selecting part 906 selectively outputs the I and Q
signals of one band among the I and Q signals of the first and
second bands, which are respectively outputted from the first band
signal filtering part 914 and the second band signal filtering part
915. The power calculating part 907 calculates the power of the
pilot signal by using the I signal outputted from the selecting
part 906. The comparing part 908 compares the power of the pilot
signal with a preset threshold value and generates a control signal
for selecting one of the output signals of the first and second
band signal filtering parts 914 and 915. The frequency/phase error
detecting part 916 includes a delay unit 909, a code detector 910
and a multiplier 911 and detects a frequency/phase error component
of the I and Q signals outputted from the selecting part 906. The
loop filter 912 removes an RF component from the frequency/phase
error component, which is outputted from the frequency/phase error
detecting part 916. The VCO (or NCO) 913 changes an oscillation
frequency according to the frequency/phase error component whose RF
component is removed.
[0114] The first bandwidth and the second bandwidth of the third
embodiment have the same range as those of the first embodiment.
The selecting part 906 passes the signal of a frequency bandwidth
where the pilot signal is contained among the I signal outputted
from the first LPF 902 of the first bandwidth and the first LPF 904
of the second bandwidth, and the power calculating part 907
calculates the power of the pilot signal and transmits it to the
comparing part 908.
[0115] The comparing part 809 compares the power of the pilot
signal with the preset threshold value. If the power of the pilot
signal is greater than the threshold value, the comparing part 809
generates the control signal for selecting the first band signal
filtering part 914. If the power of the pilot signal is less than
the threshold value, the comparing part 808 generates the control
signal for selecting the second band signal filtering part 915.
[0116] The selecting part 906 outputs the baseband I and Q signals,
which are outputted from one of the first and second band signal
filtering parts 914 and 915 according to the control signal of the
comparing part 908, to the frequency/phase error detecting part
916.
[0117] Then, the frequency/phase error detecting part 916 outputs a
frequency/phase error detecting component (control component) to
the loop filter 912. The loop filter 912 removes RF component
contained in the frequency/phase error component and outputs the
resulting signal to the VCO 913. The VCO 913 changes the
oscillation frequency according to the controlled voltage and
outputs to the complex multiplier 901. At this point, the selected
band signal filtering part 914 or 915, the frequency/phase error
detecting part 916, the loop filter 912 and the VCO 913 operate as
the FPLL.
[0118] Compared with the first and second embodiments, the third
embodiment can automatically select the necessary bandwidth by
using a few elements and can also stabilize the receiver much more
under fast changing channel conditions.
[0119] FIG. 10 is a block diagram of a carrier recovery part of a
digital TV receiver according to a fourth embodiment of the present
invention.
[0120] Referring to FIG. 10 the carrier recovery part of the
digital TV receiver includes a complex multiplier 1001, an FPLL
1030, and a gain control part 1020.
[0121] If the passband analog signal is converted into the digital
signal, a Hilbert transformer (not shown) shifts the signal by
90.degree. such that the digital signal is transformed into a Q
signal of an imaginary component. A delay unit (not shown) delays
the digital signal by a predetermined time when the digital signal
is transformed into the Q signal at the Hilbert transformer, and
then outputs an I signal of a real component. The complex
multiplier 1001 multiplies the I and Q signals by an output signal
of a VCO (or NCO) 1011 to output a baseband I signal and a baseband
Q signal (carrier wave). The FPLL 1030 includes a frequency locked
loop (FLL) for locking a frequency of the baseband I signal and a
phase locked loop (PLL) for locking a phase of the Q signal. The
FLL is configured with a first LPF 1004, a delay unit 1006, a code
detector 1007, a multiplier 1008, a loop filter 1010 and a VCO
1011. The PLL is configured with a second LPF 1005, the multiplier
1008, the loop filter 1001 and the VCO 1011. The gain control part
1020 includes a power calculator 1009, a comparator 1012, and first
and second gain controllers 1002 and 1003. The power calculator
1009 calculates a pilot power of the I signal outputted from the
first LPF 1004, and the comparator 1012 compares the pilot power of
the I signal with a preset threshold value. The first and second
gain controllers 1002 and 1003 are configured between the complex
multiplier 1001 and the LPFs 1004 and 1005 and controls power of
the pilot signal for recovering the carrier wave by adjusting the
gain of the I and Q signals outputted from the complex multiplier
1001 according to the comparison result of the comparator 1012, and
then outputs it to the FPLL 1030.
[0122] A basic structure of the fourth embodiment is similar to
that of FIG. 3. However, when the carrier recovery part recovers
the carrier wave, a digital processing part selects a desired
channel frequency through an antenna, converts the channel
frequency into an intermediate frequency, and digitalizes it by
passing a predetermined band of the intermediate frequency. Then,
the power value of the signal outputted from the first LPF 1004 for
removing unnecessary signals among the passband signal in the
carrier recovery is compared with the preset reference or threshold
value. Then, the carrier wave is recovered by setting the pilot
component of the digitalized passband signal to the desired gain
according to the comparison result. In addition, since a clock
demodulation part for removing the pilot signal and extracting a
synchronizing signal, a noise removing part for removing a linear
noise and a residual phase jitter of the baseband signal by using
the synchronizing signal, and a decoding part (for example, an FEC
part) for decoding the baseband signal, whose noise is removed,
have the same structures as the general TV receiver, a detailed
description thereof will be omitted.
[0123] As described above, the FPLL algorithm performs the carrier
recovery based on the pilot signal. Accordingly, the first LPF 1004
is used to remove data component unnecessary in the carrier
recovery, and the power calculator 1009 calculates the power of the
pilot signal outputted from the first LPF 1004.
[0124] The gain control parts 1002 and 1003 controls the gain of
the input signals of the first and second LPFs 1004 and 1005 (that
is, the I and Q output signals) by using the pilot power.
[0125] Therefore, the gain of the input signals of the LPFs can be
controlled according to the degree of the signals outputted from
the first and second LPFs 1004 and 1005, which are reduced as the
power of the pilot signal gets weak. In normalizing the gain
control of the input signals according to the pilot power of the
signal inputted to the first and second LPFs 1004 and 1005, even
when the pilot power becomes weak due to the linear noise, the
first and second LPFs 1004 and 1005 can receive the pilot signal
having a predetermined power. It means that the entire gain of the
FPLL loop can rise by increasing the pilot signal having the weak
power.
[0126] FIG. 11 is a block diagram of a carrier recovery part of a
digital TV receiver according to a fifth embodiment of the present
invention.
[0127] Referring to FIG. 11, the carrier recovery part of the
digital TV receiver includes a complex multiplier 1101, an FPLL
1130, and a gain control part 1120.
[0128] If the passband analog signal is converted into the digital
signal, a Hilbert transformer (not shown) shifts the signal by
90.degree. such that the digital signal is transformed into a Q
signal of an imaginary component. A delay unit (not shown) delays
the digital signal by a predetermined time when the digital signal
is transformed into the Q signal at the Hilbert transformer, and
then outputs an I signal of a real component. The complex
multiplier 1101 multiplies the I and Q signals by an output signal
of a VCO (or NCO) 1111 to output a baseband I signal and a baseband
Q signal (carrier wave). The FPLL 1130 includes a frequency locked
loop (FLL) for locking a frequency of the baseband I signal and a
phase locked loop (PLL) for locking a phase of the Q signal. The
FLL is configured with a first LPF 1102, a delay unit 1104, a code
detector 1105, a multiplier 1106, a loop filter 1110 and a VCO
1111. The PLL is configured with a second LPF 1103, the multiplier
1106, the loop filter 1110 and the VCO 1111. The gain control part
1120 includes a power calculator 1107, a comparator 1108, and a
gain controller 1109. The power calculator 1107 calculates a pilot
power of the I signal outputted from the first LPF 1102, and the
comparator 1108 compares the pilot power of the I signal with a
preset threshold or reference value. The gain controller 1109
receives the output of the multiplier 1106 and the output of the
comparator 1108, controls gain of the frequency/phase error
component outputted from the multiplier 1106, and outputs it to the
loop filter 1110.
[0129] In the fifth embodiment, the complex multiplier 1101
actually outputs the I and Q signal of the carrier recovery
part.
[0130] At this point, when the gain of the first LPF 1102 is "1",
the code detector 1105 does not influence the gain of the signal at
all. Thus, the gain controller 1109 of FIG. 11 is equivalent to
that of FIG. 10 in which the gain controller is disposed at a next
stage of the multiplier.
[0131] In FIG. 11, it can be considered that the gain controller
1109 controls the gain of the multiplier (error detector) 1106.
Also, when the pilot signal is weak, the entire gain is controlled
by increasing the gain of the error extracted by the multiplier
1106.
[0132] FIG. 12 is a block diagram of a carrier recovery part of a
digital TV receiver according to a sixth embodiment of the present
invention.
[0133] Referring to FIG. 12, the carrier recovery part of the
digital TV receiver includes a complex multiplier 1201, a first
band pilot signal filtering part 1215, a second band pilot signal
filtering part 1216, a selecting part 1206, a frequency/phase error
detecting part 1217, a power calculating part 1207, a comparing
part 1208, a gain control part 1212, a loop filter 1213, and a VCO
1214.
[0134] The complex multiplier 1201 receives an I signal and a Q
signal from a delay unit (not shown) and a Hilbert transformer (not
shown), multiplies the I signal and the Q signals by an output
signal of the VCO 1214, and outputs a baseband I signal and a
baseband Q signal (carrier wave). The first band pilot signal
filtering part 1215 includes first and second LPFs 1202 and 1203
having a first bandwidth and outputs a pilot signal component of a
first band among the baseband I and Q signals outputted from the
complex multiplier 1201. The second band pilot signal filtering
part 1216 includes first and second LPFs 1204 and 1205 having a
second bandwidth and outputs a pilot signal component of a second
band among the baseband I and Q signals outputted from the complex
multiplier 1201.
[0135] The selecting part 1206 selectively outputs the I and Q
signals of one band among the I and Q signals of the first and
second bands, which are respectively outputted from the first band
pilot signal filtering part 1215 and the second band pilot signal
filtering part 1216. The frequency/phase error detecting part 1217
includes a delay unit 1209, a code detector 1210 and a multiplier
1211 and detects a frequency/phase error component from the I and Q
signals outputted from the selecting part 1206. The power
calculating part 1207 calculates the power of the pilot signal at
the signal outputted from the selecting part 1206. The comparing
part 1208 compares the power of the pilot signal with a preset
threshold or reference value. Then, the comparing part 1208
generates a control signal for selecting one of the output signals
of the first and second band pilot signal filtering parts 1215 and
1216 to the selecting part 1206. Also, the comparing part 1208
generates a control signal for controlling gain of the output
signal of the frequency/phase error detecting part 1217 to the gain
control part 1212. The gain control part 1212 controls the gain of
the frequency/phase error component outputted from the
frequency/phase error detecting part 1217 according to the
comparison result of the comparing part 1208. The loop filter 1213
removes an RF component from the frequency/phase error component,
which is outputted from the gain control part 1212. The VCO 1214
changes an oscillation frequency according to the frequency/phase
error component whose RF component is removed.
[0136] The first bandwidth and the second bandwidth of the sixth
embodiment have the same range as those of the first embodiment.
The selecting part 1206 passes the signal of a frequency bandwidth
where the pilot signal is contained among the I signals outputted
from the first LPF 1202 of the first bandwidth and the first LPF
1204 of the second bandwidth, and the power calculating part 1207
calculates the power of the pilot signal and transmits it to the
comparing part 1208. The comparing part 1208 compares the power of
the pilot signal with the preset threshold value. If the power of
the pilot signal is greater than the threshold value, the comparing
part 1208 generates the control signal for selecting the first band
pilot signal filtering part 1215. If the power of the pilot signal
is less than the threshold value, the comparing part 1208 generates
the control signal for selecting the second band pilot signal
filtering part 1216. In addition, the comparing part 1208 allows
the gain control part 1212 to control the gain of the pilot power
according to the comparison result. At this point, it is possible
when the gain control of the gain control part 1212 is normalized
corresponding to the output signals of the first and second LPFs
1204 and 1205 of the second bandwidth, which are reduced as the
pilot power gets weak. That is, it means that the entire gain of
the FPLL loop can rise by increasing the pilot signal having the
weak power.
[0137] Then, the selecting part 1206 outputs the baseband I and Q
signals, which are outputted from one of the first and second band
pilot signal filtering parts 1215 and 1216, to the frequency/phase
error detecting part 1217 according to the control signal of the
comparing part 1208.
[0138] The frequency/phase error detecting part 1217 outputs the
frequency/phase error detection component (control component) to
the gain control part 1212. The gain control part 1212 controls the
gain of the frequency/phase error component according to the
comparison result of the comparing part 1208 and outputs to the
loop filter 1213. The loop filter 1213 removes RF component
contained in the frequency/phase error component and outputs the
resulting signal to the VCO 1214. The VCO 1214 changes the
oscillation frequency according to the controlled voltage and
outputs to the complex multiplier 1201. At this point, the selected
pilot signal filtering part 1215 or 1216, the frequency/phase error
detecting part 1217, the loop filter 1213 and the VCO 1214 operate
as the FPLL.
[0139] As described above, since the gain of the FPLL loop and the
bandwidth of the LPFs are automatically controlled according to the
received pilot power, the carrier recovery can be more stably
performed even when the pilot signal is weak.
[0140] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention.
Thus, it is intended that the present invention covers the
modifications and variations of this invention provided they come
within the scope of the appended claims and their equivalents.
* * * * *